1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system and, more particularly, to a sheet folding operation.
2. Description of the Related Art
In recent years, there has been a tendency to promote information computerization, and image processing apparatuses, such as printers or facsimile machines that are used to output computerized information or scanners that are used to computerize documents, are essential apparatuses. Such an image processing apparatus has an image capturing function, an image forming function, a communication function, or the like, so that it is often configured as a multifunction peripheral that can be used as a printer, facsimile machine, scanner, or copier.
Out of the above multifunction peripherals, there are known multifunction peripherals that include a folding processing apparatus that, after an image formation is performed on a fed sheet so that an image is drawn, performs a folding operation on the sheet on which the image has been formed. If a sheet is subjected to a folding operation by the above folding processing apparatus, and if it remains so, a fold line is loose and incomplete, which results in a state where the height of the folded part is high.
Therefore, out of the above multifunction peripherals, there are known multifunction peripherals that include, in addition to a folding processing apparatus, a fold-enhancing apparatus that performs a fold-enhancing operation to enhance a fold line that is formed during a folding operation by pressing the fold line, whereby the fold line is enhanced and the height of the folded part is reduced (for example, see Japanese Patent Application Laid-open No. 2004-075271).
Such a fold-enhancing apparatus includes a pair of fold-enhancing rollers that are made up of two fold-enhancing rollers that are laterally bridged in a direction parallel to a fold line that is formed by the folding processing apparatus, and the pair of fold-enhancing rollers nip the fold line, which is formed by the folding processing apparatus, on both sheet surfaces, thereby pressing the fold line.
Alternatively, such a fold-enhancing apparatus includes a fold-enhancing roller, which is laterally bridged in a direction parallel to a fold line formed by the folding processing apparatus, and a sheet supporting plate that supports a sheet on the sheet surface, and the fold-enhancing roller and the sheet supporting plate nip the fold line that is formed by the folding processing apparatus on both sheet surfaces, thereby pressing the fold line.
Here, in the fold-enhancing apparatus, a force acts to press the fold-enhancing roller and the sheet supporting plate against each other at both ends thereof in a main-scanning direction, whereby a pressing force is generated over the entire area in the main-scanning direction.
Therefore, in the above fold-enhancing apparatus, when a fold line is pressed, resilience is generated from the sheet in response to the pressing force; however, in the vicinity of both ends in the main-scanning direction, the force for pressing the fold-enhancing roller and the sheet supporting plate against each other acts as a force that resists the above-described resilience, and therefore a fold line can be sufficiently pressed with the force even though the resilience is received.
However, there is a problem in that there is no force that can resist the above-described resilience in the vicinity of the central part in the main-scanning direction; therefore, if resilience is received, the fold-enhancing roller and the sheet supporting plate are bent in the direction opposite to the pressing direction, and a fold line cannot be sufficiently pressed.
In view of the above, there is a need to effectively enhance a fold line that is formed on a sheet.